1. Field of the Invention
This invention relates generally to alternating-current transformer devices, and more particularly, but not by way of limitation, to an improved adjustable transformer and switching device for relatively high voltage applications, such as providing varying voltage outputs for energization of oil field equipment and the like.
2. Description of the Prior Art
The prior art includes many types of adjustable transformers which include means for adjustment, not only in the secondary but in the primary, or in both windings. The prior art devices have used tapping or switching output structures for selecting the transformer turns ratio, and therefore, for obtaining a selected voltage transformation, but most of such transformer devices have done so by merely selecting a certain portion of the overall windings in accordance with desired output characteristics. Such devices, in relatively random selection of parts of the overall windings, have failed to optimize minimization and uniformity of core and winding losses in order to effect more efficient use of the volume of winding and core space, a consideration which becomes particularly important in high voltage energization applications as here contemplated relative to the present invention.
In U.S. Pat. No. 3,083,331 to M. A. Spurway, a transformer construction is proposed in which a multiple winding primary (or secondary) is utilized in the transformer with a selective switching arrangement in which the multiple windings thus provided can be seriesed or paralleled in the primary circuit to varying degrees to provide a selective output. In the Spurway transformer, the multiple windings of the primary are disposed symmetrically in relation to the secondary, and under all conditions of operation of the transformer, the leakage impedances of corresponding sections of the primary windings, as interconnected by the switch in respect to each other, are equal. The switching arrangement allows sections of the multiple windings to be selectively interconnected so that progressive variation is obtained from a wholly electrical series connection of the windings with each other, to a wholly electrical parallel connection.
While the Spurway series-parallel transformer winding arrangement provides good selective control of output voltage over a wide range of voltages, and reduces core and winding losses, its construction necessarily contemplates the placement of the several windings or sections of the primary around the core of the transformer by extending these windings or sections in opposite directions around the core in order to achieve the desired symmetry in respect to the secondary winding. This is necessary in order to maintain the leakage impedance through interconnected parts of the two primary windings or sections at an equal value.